In the semiconductor industry, various manufacturing processes are typically carried out on a workpiece (e.g., a semiconductor substrate) in order to achieve various results on the workpiece. Processes such as ion implantation, for example, are performed in order to obtain a particular characteristic within the workpiece, such as a specific bulk resistivity or a limited diffusivity of a dielectric layer on the workpiece by implanting a specific type of ion.
In a typical serial implantation process, a single workpiece is implanted at a time by an ion beam, which could be a pencil ion beam or spot ion beam generally scanned back and forth with respect to the workpiece or a broad ribbon beam, therein facilitating implanting or doping all of the workpiece with ions. In a mechanically scanned implantation system, the workpiece is mechanically scanned through a stationary ion beam in a fast scan direction while stepping with slower velocity in a transverse direction with respect to the ion beam, e.g. in a slow scan direction, therein effectively implanting a portion or “strip” of the workpiece each time it passes through the ion beam in the fast scan direction.
In what is called a “hybrid” scan ion beam implantation system, the ion beam is scanned (e.g., using an electric scanner) in the fast scan direction along one axis, therein defining a scanned ribbon beam having a given length (often called a scan width). Accordingly, the workpiece is typically mechanically scanned through the scanned ribbon beam in the slow scan direction that is generally orthogonal to the ribbon beam, therein uniformly distributing the beam over the workpiece. The scanned ion beam effectively implants a portion or “strip” of the workpiece each time it passes across the workpiece in the fast scan direction, wherein a length of the scanned path of the ion beam typically exceeds the diameter of the workpiece (commonly called “overshoot” or “overscan”) in order to uniformly dope the workpiece with ions.
Throughput of workpieces through the ion implantation system is commonly a function of the ion beam utilization, which is defined by the amount of dopant implanted to the workpiece versus the total amount of dopant output by the ion beam over a given time period. Attempts have been made to maximize the ion beam utilization of hybrid scan ion implanters by determining an optimum scan width of the ribbon beam. One difficulty, however, is that the scan width of the ribbon beam is typically fixed for a given ion implanter, whereby the scan width has to be wide enough to implant a workpiece of maximum size (along with the proper amount of overscan) in order to provide a uniform implantation. Since many workpieces have diameters that are less than the diameter of the maximum-sized workpiece, (e.g., a generally circular workpiece), maintaining such long scan widths for workpieces that are smaller than the maximum-sized workpiece can often result in poor ion beam utilization.
Furthermore, the ion beam is conventionally profiled during implant setup, wherein a size of the ion beam and the optimal scan width is determined such that the fixed scan width ensures an adequate implant and overshoot across the entire workpiece in order to provide acceptable implant uniformity. Such profiling, however, typically includes one or more diagnostic and/or calculation procedures, therein adding time to the implant setup. The additional time taken for profiling the ion beam during implant setup often counteracts or negates the reduction in implant time achieved by optimizing the scan width, thus, adversely affecting workpiece throughput.